Unable to use the tool "difference" after the tool "clip"

Question

I have stumbled on an error and I would like to have an external point of view to maybe help me figure it out.

When I

1. clip layerA as input with layerB as the overlay, and then
2. make the difference of layerC as input with the Clipped layer as the overlay layer,

I get this error:

Could not add feature with geometry type MultiLineString to layer of type MultiPolygon

Strangely, all of the layers are multipolygons.

I then tried to do mutlipart to singlepart + remove duplicate vertices + fix geometries, but the issue still arise. I even tried to do a tiny negative buffer to make very small objects disapear.

Any other idea to circumvent this situation?

Here is a link to the gpkg containing the layers : https://drive.google.com/drive/folders/1TpPflqDJGYriDaYcjr49F04qpk9uXsPw?usp=share_link

I use Windows11 and QGIS 3.28.6

Answer 1

Buffer layer C with a very small value, then it works. I used 0.01 m as buffer distance. Buffer again with the negative of it (-0.01) to get back the initial shape, but without the gaps contained in layer C.

Answer 2

Apologies for cluttering the answer section, but this is geared towards why the OP might be running into some problems and may lend a hand towards others troubleshoot similar problems.

The OP has some odd geometry types within their dataset. For example LayerC id==27 is Class NoneType. You can find these underlying issues by using geopandas within a python script.

# python 3.10.9
import os
os.environ['USE_PYGEOS'] = '0'
import geopandas

# Load the file
file = geopandas.read_file("C:/Users/zleslie/Downloads/layerC.shp")

# Iterate through geometries and track the id with enumerate
for i, geom in enumerate(file.geometry):
    try:
        geom.geom_type
    except:
        print(type(geom))
        print(i)

Answer 3

I suggest you run select by expression on your faulty layer (in this case layer C), using $area<1, thus selection all sliver geometries. Then delete those.

This can be implemented in a model, probably in a script, too, but the latter is beyond my expertise.